One good way to hunt is to use calm spell on your prey. I shoot a calm on the deer, then soul trap spell, then calm again, then kill it however you want it.
I love you for this.
Nightblade is my default playing style. Don't forget skill trainers is my advice. You'll want both levels of augmented frost and flames, and fire and frost enchanter perks. That way you can both enchant armour with enough resistance to those two elements to handle dragons, and enchant your weapons to deal massive single-blow damage.
Additionally, go ahead and take Extra Pockets, and if you're willing to get to that level for the perks (grinding pickpocket to 100 is easy, trust me, the issue is perk level), perfect touch is good for assuring a 1hko against bosses in heavy armour, assuming you don't get caught pickpocketing. Probably not worth it for the benefit, but I always optimise for level 81.
GET SHADOW WARRIOR, FIGHTING STANCE AND CRITICAL CHARGE. Learn to use them together with stealth rolls. It's the best damage you can get in a single shot I believe. Also it makes you a ninja, who doesn't want to be a ninja.
Drop Master Illusion. The master level illusion spells aside from the rally version are all pretty much useless, since you can't dual wield them and thus hit any level cap, making them worlds weaker than the Expert- and Adept-level spells. The rally one is neat if you are playing the civil war questline, but pretty much useless for a nightblade. Thus, since you'll never be using those spells, the perk is useless.
Lastly, I'd invest a bit in alteration for paralysis, but that's a personal flavour choice. Note that whatever you do, dragons will be tough if not impossible to manage at higher levels.
EDIT: Smithing is also advisable to improve your weapons. Forgot about that. Only go up the heavy line to Daedric, and maybe get Arcane Blacksmith.